1. Field of the Invention
This document relates to a liquid crystal display module, and more particularly, to a liquid crystal display module, which can prevent corrugations of a reflection plate, and an assembling method thereof.
2. Related Art
In a recent information-oriented society, the importance of display devices used as visual information conveying media has been emphasized. However, cathode ray tubes or Braun tubes that have been widely used have major disadvantages in regard to their large size and weight. There has therefore been developed various types of flat display apparatuses capable of overcoming the disadvantages of cathode ray tubes.
Examples of currently commercially available flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electroluminescence display (EL).
Among them, liquid crystal displays (LCDs) show a tendency that their application fields are gradually increased due to the characteristics of light weight, thin thickness, low-power-consumption driving, and so on. With this trend, the LCDs are used as displays for portable computers such as laptop computers, office automation devices, audio/video devices, indoor/outdoor advertising display devices, and the like. The LCDs display a desired picture on a screen by controlling the transmissivity of light beam in accordance with a video signal applied to a plurality of control switches arranged in a matrix. The LCDs have been rapidly developed to larger sizes and higher resolutions due to improvements in mass production technology and the fruitful result of research and development.
In general, a liquid crystal display (LCD) comprises a liquid crystal display module (LCM) and a driving circuit unit for driving the liquid crystal display module.
The liquid crystal display module comprises a liquid crystal panel in which liquid crystal cells are arranged in matrix between two sheets of glass substrates, and a backlight unit for irradiating light to the liquid crystal panel. The liquid crystal panel and the backlight unit should engage with each other in an integral shape to prevent light loss and have protection from a damage caused by an external impact. Thus, a case for the LCD enclosing the back light unit including the edge of the liquid crystal panel is provided.
There are two types of backlight units for a liquid crystal display module: a direct-below-type, and an edge-type. The edge-type backlight unit has a light source installed on the outside of a flat panel, and thus the light from the light source is incident to the entire surface of the liquid crystal panel by using a transparent light guide plate. The direct-below-type backlight unit has a light source arranged at a rear surface of the liquid crystal panel, and the light source directly radiates light to the liquid crystal panel.
FIG. 1 shows a cross sectional view of a light incident portion of a conventional liquid crystal display module employing an edge type backlight unit. FIG. 2 shows an assembly order of the conventional liquid crystal display module.
Referring to FIGS. 1 and 2, with regards to the assembly order of the conventional liquid crystal display module, first, a support main 2 for supporting the entire liquid crystal display module is assembled, and then a light source assembly 10 having a light source FPC (flexible printed circuit) 9 attached thereto is mounted on a projecting, lower stepped face of the support main 2. Next, a light guide plate 11 for converting a light from the light source assembly 10 into a surface light source is mounted on a projecting, lower stepped face of the support main 2. And, a reflection plate 12 for reflecting a light, which progresses to a lower surface and side surfaces of the light guide plate, to the upper surface is mounted on a recessed, lower stepped face of the support main 2, and then a cover bottom 13 is fixed to the bottom surfaces of the light source assembly 10 and light guide plate 11 by engagement. Next, a plurality of optical sheets 8 for controlling a diffusion and a direction of travel of the light passing through the light guide plate 11 is mounted on the light guide plate 11. A light blocking tape 7 is attached onto the optical sheets 8 and a projecting, upper stepped face the support main 2 to prevent light loss. A liquid crystal panel 5 including upper and lower array substrates 3 and 4 and a liquid crystal panel assembly consisting of upper and lower polarizing plates 6a and 6b are mounted on the light blocking tape 7, and then a case top 1 for surrounding the edge of the liquid crystal panel assembly is fastened.
However, such a conventional liquid crystal display module has the following problems.
First, the conventional liquid crystal display module is problematic in that corrugations are generated on the reflection plate 12 when an operation test is conducted in a high-temperature or high-humidity environment. These corrugations are caused by the facts that the probability of exposure to thermal expansion is high because the reflection plate 12 is arranged adjacent to the light source assembly 10 having relatively high heat generation, and that there are a lot of constraining points P1, P2, and P3 between the reflection plate and other equipment items 2, 10, and 11 as the liquid crystal display module is assembled in a reverse assembly order as shown in FIG. 2. The corrugations of the reflection plate 12 tends to become larger if there occurs a burr of the other equipment items targeted by the constraining points P1, P2, and P3 or a problem of dimensional management of these equipment items.
Second, to alleviate the constraining points P1, P2, and P3, there is a need to manage the dimensions, such as i) a height A of the mounting end of the reflection plate 12 of the support main 2, ii) a gap B between the light source assembly 10 and the reflection plate 12, and iii) a gap B between the light guide plate 11 and the reflection plate 12, within a range of generating no constraint. There is a limitation in managing the dimensions due to the aforementioned reverse assembly process and the light guide plate 11's pressing against the reflection plate 12 caused by self-weight.